The present invention relates to the field of angioplasty. In particular, the present invention relates to a dilatation balloon catheter of the "over-the-wire" type.
Angioplasty has gained wide acceptance in recent years as an efficient and effective method for treating types of vascular disease. In particular, angioplasty is widely used for opening stenoses in the coronary arteries, although it is also used for treatment of stenoses in other parts of the vascular system.
The most widely used form of angioplasty makes use of a dilatation catheter which has an inflatable balloon at its distal end. Typically, a hollow guide catheter is used in guiding the dilatation catheter through the vascular system to a position near the stenosis (e.g., to the aortic arch). Using fluoroscopy, the physician guides the dilatation catheter the remaining distance through the vascular system until the balloon is positioned across the stenosis. The balloon is then inflated by supplying a fluid under pressure through an inflation lumen to the balloon. The inflation of the balloon causes stretching of the artery and pressing of the lesion into the artery wall to reestablish acceptable blood flow through the artery.
There has been a continuing effort to reduce the profile and shaft size of the dilatation catheter so that the catheter not only can reach but also can cross a very tight stenosis. A successful dilatation catheter must also be sufficiently flexible to pass through tight curvatures, especially in the coronary arteries. A further critical requirement for a successful dilatation catheter is its "pushability". This involves the transmission of longitudinal force along the catheter from its proximal end to its distal end so that a physician can push the catheter through the vascular system and the stenosis. In addition, a rotation ("twist" or "torque") of the catheter shaft at its proximal end should be evenly translated by the catheter to its distal end so that torque does not build up in the catheter which might cause it to rapidly unwind at its distal end during use.
Two commonly used types of dilatation catheters are referred to as "over-the-wire" catheters and "non-over-the-wire" catheters. An over-the-wire catheter is one in which a separate guide wire lumen (sometimes called a "thru lumen") is provided so that a guide wire can be used to establish the path through the stenosis. The dilatation catheter can then be advanced over the guide wire until the balloon is positioned within the stenosis. One problem with the over-the-wire catheter is the requirement of a larger profile and a generally larger outer diameter along its entire length in order to allow for a separate guide wire lumen.
A non-over-the-wire catheter acts as its own guide wire, and thus there is no need for a separate guide wire lumen. One advantage of a non-over-the-wire catheter is its potential for a reduced outer diameter along its main shaft since a guide wire lumen is not required. However, one disadvantage is the inability to maintain the position of a guide wire within the vascular system when removing the catheter and exchanging it for one of a smaller (or larger) balloon diameter. Thus, to accomplish an exchange with the non-over-the-wire catheter, the path to the stenosis must be reestablished when replacing the catheter with one having a different balloon diameter.
A recent innovation in non-over-the-wire catheters is to employ a thin wall metal tube, such as an hypodermic tubing, for at least a proximal portion of the main shaft of the catheter. Using a long and narrow thin wall metal tube provides enhanced pushability for such catheters. Examples of non-over-the-wire catheters that use a metal tube shaft are seen in Keith et al. U.S. Pat. No. 4,838,268, issued June 13, 1989, and in PCT Publication No. WO86/06285, published Nov. 6, 1989. Flexibility is not as great as concern in the proximal portion of the catheter shaft, and particularly that portion thereof which is passing through the guide catheter. It is the distal portion of the catheter shaft which must negotiate the tortuous portions of the arteries in the vascular system in order to reach the lesion. Of course, reducing the profile and shaft size of a catheter is a continuing concern, and the use of thin wall metal tubing also assists in attaining these ends.
In over-the-wire catheters, the factors of transmit torque have not been quite as critical since the catheter is typically tracking over an existing guide wire through the vascular system. Shaft materials for over-the-wire catheters have typically consisted of polymer-based materials such as polyethylene. With the continuing emphasis on shaft size reduction and the emergence of small diameter guide wires and small diameter guide catheters, however, the reduction in shaft sizes for polymer-based shafts of over-the-wire catheters has diminished the pushability of such shafts. There is thus a need for the development of an over-the-wire catheter with a smaller diameter shaft that exhibits good characteristics of pushability, and the requisite flexibility at the distal end of the catheter to negotiate the coronary arteries.